Slab gas lasers, and in particular, slab CO2 lasers are well known and are used in a wide variety of applications including laser based cutting and engraving machines. A typical slab gas laser includes a live slab electrode and a ground slab electrode which define a primary gas discharge chamber there between. The live electrode is in electrical communication with a power supply to provide an excitation signal. A known problem with gas slab lasers is that without enough free electrons at the time of applying the excitation signal, the laser may have a plasma breakdown delay or skip some of the first pulses of laser discharge, which is undesirable when used in applications such as engraving. In order to eliminate this problem, it is known to provide free electrons to the primary gas discharge chamber upon actuation of the excitation signal in a process known as pre-ionization.
Several methods of providing pre-ionization are known, and include the use of UV lamps, DC-corona plasma formation, spark arc ionization and application of a low intensity excitation signal into the laser amplifying medium, known as a “tickle signal”. However, each of these methods of pre-ionization have recognized shortcomings, such as a limited lifespan of UV lamps, introduction of contaminant particles resulting from DC-corona plasma formation which will reduce the effective lifetime of the laser or unintended lasing action caused by application of a tickle signal.
One method to overcome these shortcomings is the use of a pre-ionization cell to provide free electrons to the gas discharge chamber. One such pre-ionization cell is shown Welsch, U.S. Pat. No. 5,434,881. Welsh teaches providing auxiliary electrodes adjacent to a primary gas discharge chamber defined between slab electrodes. Welsch teaches that providing the electrodes to form an auxiliary discharge path roughly parallel to the slab electrode surfaces can provide electrons into the region of the gas discharge path between the slab electrodes to provide improved ignitability of the discharge therein. Welsch teaches that a plurality of the auxiliary electrodes may be distributed along the electrode surfaces, that the auxiliary discharges therefrom can be pulsed and that the auxiliary discharges can be made continuously or ignited synchronously with the main discharge. However, the pre-ionization cell taught by Welsch is not without shortcomings of its own. In particular, Welsch teaches aligning the ground slab electrode with the ground electrode of the pre-ionization cell and the live slab electrode with the live electrode of the pre-ionization cell. This arrangement can lead to cross-talking between an amplifier driving the live slab electrode and the amplifier driving the live electrode of the pre-ionization cell, disrupting operation of the amplifiers. In addition, the pre-ionization cell of Welsch risks creation of an electromagnetic field in close proximity to the primary gas discharge chamber which can interfere with the operation of the slab gas laser. The slab gas laser with a pre-ionization cell disclosed herein is intended directed toward overcoming one or more of the problems discussed above.